1. Field of the Invention
The present invention is related to a bias circuit for a read MR (Magneto-Resistive) head applied to a magnetic recording and/or reproducing apparatus, such as a HDD (Hard Disk Drive) or the like.
2. Description of the Related Art
Conventionally, in a magnetic recording and/or reproducing apparatus, such as a Hard Disk Drive for recording necessary data by magnetizing a magnetic layer formed on a rotating recording disk, a Magneto-Resistive head (MR head) is usually used to read out recorded data in a case of reading the recorded data.
Such a MR head is positioned opposite to the recording disk, and it is possible to carry out the reading of the recorded data by outputting a change of magnets in the magnetic layer of the recording disk as a change of resistive value of the MR head.
In this case, it is necessary to flow a bias current through the MR head using a bias circuit in advance, and the Voltage bias system, which controls a voltage applied to the MR head, is well-known as a bias system for such a bias circuit.
As shown in FIG. 3, a bias circuit a of the Voltage bias system is comprised of a bias current output circuit 100 for outputting the bias current flowing through the MR head Rmr and a feedback circuit 200 for controlling the output bias current from the bias current output circuit 100, so that a voltage across the MR head Rmr is controlled to be a predetermined value by detecting the voltage variation across the MR head Rmr through which the bias current is flowing.
In the magnetic recording and/or reproducing apparatus having the MR head Rmr connected to the bias circuit a, not only the read MR head Rmr but a write inductive head 400 are provided in a head body 300 that is positioned opposite to a recording disk as shown FIG. 4, and it is so configured to operate either one of the MR head Rmr or the inductive head 400.
Hereinafter, a mode where a playback of the recorded data is carried out from the recording disk by operating the MR head Rmr is called as a read (reproducing) mode, and a mode where a writing of the data is carried out to the recording disk by operating the inductive head 400 is called as a write (recording) mode.
The head body 300 is positioned opposite to the recording disk as mentioned above, and accordingly, the MR head Rmr and the bias circuit a are connected to each other by using a flexible printed circuit board 500, the inductive head 400 is connected to the recording data amplifier circuit 600, and the head body 300 is isolated from an amplifier circuit 700 which includes the aforementioned bias circuit a and the recording data amplifier circuit 600.
The flexible printed circuit board 500 has a bare essential substrate area in order to make the magnetic recording and/or reproducing apparatus as small and light-weight as possible. Further a read signal wiring 800 for connecting the MR head Rmr and the bias circuit a and a write signal wiring 900 for connecting the inductive head 400 and the recording data amplifier circuit 600 are positioned extremely close to each other.
For this purpose, when a writing signal flows through the write signal wiring 900 in the write mode, some cross-talk is sometimes generated in the read signal wiring 800 due to the writing signal, and there occurs a variation in the bias current flowing through the MR head Rmr due to the cross-talk. Accordingly, when the mode is changed from the write mode to the read mode, a recovery time is required for the bias current to be a predetermined bias current value for the read mode, so that it takes a time to start the reading operation. Therefore, in the write mode, it was usual to stop the flow of the bias current through the MR head Rmr by halting the operation of the bias circuit a.
Namely, in a changeover switch SW provided in the bias circuit a in FIG. 3, the changeover switch SW was made ON in the read mode, and the change-over switch SW was made OFF in the write mode.
In FIG. 4, a reference sign 710 designates a control signal line for transmitting control signals for transmitting the read mode for a read signal and for transmitting the write mode for a write signal to the bias circuit a, a read data amplifier 720 for amplifying the read data outputted from the bias circuit a, and further to the recording data amplifier circuit 600. In this case, it is so configured that the control signal line 710 transmits the write signal when not in the read mode and transmits the read signal when not in the write mode.
However, when the operation of the bias circuit a was halted, the following problems occurred.
Namely, when the operation of the bias circuit a is halted by setting the changeover switch SW to OFF, there occur changes in the electrical state of the regulating circuit 110 provided in the bias current output circuit 100 that is prepared in order for the bias current output circuit 100 of the bias circuit a to operate stably. Therefore, when the mode is changed from the write mode to the read mode, a recovery time is required, which is necessary for the regulating circuit 110 to comeback to a predetermined electrical state. Accordingly, it becomes difficult to carry out a stable conduction of the bias current during the recovery time, so that it is not able to start reading the recorded data immediately after the mode is changed from the write mode to the read mode.
Here, the regulating circuit 110 includes an oscillation suppressing capacitor C1 that is provided in the bias current output circuit 100 for the purpose of suppressing the oscillation of the circuit and noise elimination; and the oscillation suppressing capacitor is configured by one oscillation suppressing capacitor C1 in FIG. 3.
If the operation of the bias circuit a is halted in the write mode, the power supply to the regulating circuit 110 is also halted, and thereby, there occurs voltage variation at the oscillation suppressing capacitor C1 of the regulating circuit 110, and the changeover switch SW is made ON, because the read signal is transmitted to the bias circuit a in this condition. Then, charging and discharging of the oscillation suppressing capacitor C1 in the regulating circuit 110 occurs first, so that it becomes difficult to carry out a stable conduction of the bias current until the oscillation suppressing capacitor C1 has a predetermined voltage.
Particularly, the circuit is able to increase a noise reducing effect by using a capacitor having as large a capacity as possible as the oscillation suppressing capacitor C1, so that there is a problem that it takes a long time for the voltage of the oscillation suppressing capacitor C1 to comeback to the predetermined voltage.